Modulation system



Jan. 4,.1938. HOLLMANN 2,104,541

* MODULATION SYSTEM Filed Feb. 1, 1935 w i KEY/N6 MEANS v F I? 6 k Q 49 1-1-@-|-| l-| w .24 (ATV/N6 Min/KS M K;

T a ==f x I f 6! I I I I I I v T W H E. HOLLMANN ATTORNEY.

UNITED STATES PATENT OFFICE 2,104,541 r MODULATION SYSTEM Hans Erich Hollmann, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. 11., Berlin, Germany, a corporation of Germany Application February 1, 1935, Serial No. 4,586 In Germany January 31, 1934 4 Claims. (Cl. 250-17) In the present state of the art the amplificagenerator itself produces relaxation oscillations, tion of ultra-short wave oscillations, as furnished, by which modulation is forced on the transmitfor instance, by a retarding field generator, can ter. In accordance with the invention, the not practically be carried out in an amplifier charge of a condenser inserted in the circuit ll tube because of the inertia in the movement of of the retarding field electrodes is periodically 5 the electrons. For this reason, when operating controlled by means of a trigger relay.

with extremely short waves over a transmission Figs. 1 and 2 illustrate two different embodiline or other channel, it is necessary at the rements of the invention. ceiving end to rectify the signals before intro- The circuit shown in Fig. 1 serves for prac- 147 ducing amplification. Such amplification is tically carrying out the present method of a con-- practically limited to audio frequencies. Interstant auto modulation of a braking field genera mediate frequency amplification has not heretotor. The oscillator consists of a tube R operatfore proven satisfactory since a beat reception ing in a retarding field circuit, and of a resonance can not practically be carried out by the supersystem L which may be placed within or outside 35 position of an oscillation produced in the receivthe tube, and which will be excited in the known er, in view of the lack of the required constancy manner by the electron movement. In the cirof the frequency. Furthermore, it is not possible cuit of the braking electrode B, a glow tube GI to use undamped waves interrupted in the is inserted which is bridged by a suitably variable rhythm of the signals (so-called unmodulated condenser C for the purpose of determining and telegraphy, C. W. transmission) and radiacontrolling the modulation frequency. In order 20 tion of modulated oscillations must be relied to furnish the voltage required for feeding the upon. This means that the micro wave transmitglow tube, the tube is suitably placed at a positer, whether in transmitting telegraphic signals tive bias which, for the sake of simplicity, is dior direction finding signals, etc., must be modurectly derived from the grid voltage source Eg.

5 lated with a' constant frequency. The basic idea of the new method lies in the This constant audio-frequency modulation is fact that the braking electrode B, which will be generally carried out on the basis of the method negatively charged when the micro waves are which is also used in telephonic transmission, excited, supplies the feed voltage for the trigger whereby in place of the speech currents, a conrelay GI. A condition is thus brought about in stant audio-frequency, obtained for instance which the charging of the anode B and of the from a tone producer, is simply applied to the condenser C connected thereto can only take transmitter. A still simpler method resides in place up to the ignition voltage Ez of the trigger chopping the feed current by means of a merelay GI. As soon as the glow tube is ignited, it chanical interrupter, but the latter has the disdischarges the condenser to the value of its advantage of all mechanical, contact-establishignition voltage E1 whereupon a new charging ing devices, namely that its contacts are subtakes place, and so forth. In this way the voltjected in time to considerable wear and tear. age at the braking electrode B fluctuates between I was t t ha t dvant g w s ov rthe two voltage values E2 and E1, thus modulating m y a wn m d. according t w i h the transmitter with the frequency of the relaxthe retarding field generator excites, in view of ation oscillations hereby produced. 40 its falling Current Vo age characteristic, a res- In order to more distinctly characterize the Chance System O y frequency inserted in the nature of the relaxation oscillations produced retarding fi Circuit whereby the transmitter in this manner, the difference between the ordiis likewise modulated. This method involves nary relaxation circuit will now be explained and 4 great (11111011113185, Since the adjustment Of he can also be recognized in the circuit shown. The falling c rr n vol regions is extremely critiordinary relaxation circuit operates, as is known, cal. Also, it does not conform to the optimum t a t t charging Voltage charging Working conditihhs of the trahshlitter with the condenser C across a special ohmic resistance gard to the E Wave q q W0 which may, in special cases, also be a vacuum All these difficulties are ehmmated 1n asimple tube The relaxation period is then established manner by means of the present invention, in by the known formula that the retarding field generator is combined E with a relaxation circuit, and that, by means of T=WXC a glow tube or any other trigger relay which may 3 also consist of electron tubes, the retarding field In principle, the relaxation period in the present 55 {to high frequency in parallel or in necessarily follows therefrom, as a condition, for the initiation of the relaxation oscillations, the

requirement that the inner resistance of theglow tube G! must be small as compared with the inner resistance Wrb of the generator which takes the place of the charging resistance. Only in this case is the discharge period short as compared with the charging period, otherwise a stable condition of equilibrium would be established between the charging and the discharge current.

Thus, the formula given denotes that the relaxation period of Wib must be dependent upon the E. M. F. in the braking circuit. Both values, however, are a function of the condition of excitation ofthe retarding field transmitter, and it follows therefrom that the relaxation period must likewise change to a certain degree when the operating condition changes. Where particular stress is to'be laid upon constancy of the modulation frequency, the relaxation oscillations can be stabilized by means of a resonance system S (Fig. 2) placed in series to the glow tube and tuned to the relaxation frequency.

If the transmitter is to be keyed, for instance, for purposes of telegraphy, the glow tube may be suitably switched in and shut off, as by the keying means M whereby an especially dependable initiation of the relaxation oscillations. is assured. The modulation method described in the'present example, for a transmitter with a single oscillator tube, can, as is obvious, be also readily applied to multi-tube transmitters, whether the individual tubes operate with regard push-pull.

What is claimed is:

1. In combination, an electron discharge device comprising a cathode, anode and control electrode, means including a source of potential for supplying a high positive potential to said control electrode and a much lower potential to said anode relative to said cathode, whereby there is pendulum motion of electrons about said control electrode, a pair of parallel wires for feeding energy from said source to said anode and to said control electrode respectively, a condenser bridged across said wires to form with said wires a resonance system, and the parallel combination of a condenser and a second electron discharge device located in circuit between said source and said wire which feeds energy to said anode, said last device, being of the gas-filled type providing a discharge path for its parallelly connected condenser whenever the charge thereon exceeds the critical ignition value of said device.

2. In combination, an oscillation generator of the retarding field type, said generator having a cathode, a grid and a plate comprised in an electron discharge tube and a source of potential so connected to said electrodes that the grid is maintained highly positive with respect to the other electrodes, a resonant circuit connected between the grid and plate, a capacitor connected between the plate and a suitable point on said source of potential, and means including a gaseous discharge tube in shunt with the last said capacitor for causing the oscillations of said generator to be rhythmically modulated.

3. In a system for modulating the output of a retarding field generator, an electron discharge tube having a cathode, a plate, and an intermediate electrode maintained at a high positive potential with respect to the other electrodes, a resonant network interconnecting the electrodes of said tube, means including a direct current source for maintaining said potentials on said electrodes,

a capacitor connected between a tap on said source and a portion of said resonant network leading to said plate, a gaseous discharge tube, and means including a key for at times causing said gaseous discharge tube to be shunted across said capacitor, thereby to modulate the output energy of said generator.

4. A system in accordance with claim 3 and comprising a resonant network interposed in circuit between said key and said gaseous discharge tube.

HANS ERICI-I HOLLMANN. 

